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Commit 03aa264a authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

blkcg: let blkcg core manage per-queue blkg list and counter 



With the previous patch to move blkg list heads and counters to
request_queue and blkg, logic to manage them in both policies are
almost identical and can be moved to blkcg core.

This patch moves blkg link logic into blkg_lookup_create(), implements
common blkg unlink code in blkg_destroy(), and updates
blkg_destory_all() so that it's policy specific and can skip root
group.  The updated blkg_destroy_all() is now used to both clear queue
for bypassing and elv switching, and release all blkgs on q exit.

This patch introduces a race window where policy [de]registration may
race against queue blkg clearing.  This can only be a problem on cfq
unload and shouldn't be a real problem in practice (and we have many
other places where this race already exists).  Future patches will
remove these unlikely races.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4eef3049

block/blk-cgroup.c

+56 −16
Original line number Diff line number Diff line
@@ -596,8 +596,11 @@ struct blkio_group *blkg_lookup_create(struct blkio_cgroup *blkcg, 
	/* insert */

	spin_lock(&blkcg->lock);

	swap(blkg, new_blkg);



	hlist_add_head_rcu(&blkg->blkcg_node, &blkcg->blkg_list);

	pol->ops.blkio_link_group_fn(q, blkg);

	list_add(&blkg->q_node[plid], &q->blkg_list[plid]);

	q->nr_blkgs[plid]++;



	spin_unlock(&blkcg->lock);

out:

	blkg_free(new_blkg);
@@ -646,36 +649,69 @@ struct blkio_group *blkg_lookup(struct blkio_cgroup *blkcg, 
}

EXPORT_SYMBOL_GPL(blkg_lookup);



void blkg_destroy_all(struct request_queue *q)

static void blkg_destroy(struct blkio_group *blkg, enum blkio_policy_id plid)

{

	struct blkio_policy_type *pol;

	struct request_queue *q = blkg->q;



	lockdep_assert_held(q->queue_lock);



	/* Something wrong if we are trying to remove same group twice */

	WARN_ON_ONCE(list_empty(&blkg->q_node[plid]));

	list_del_init(&blkg->q_node[plid]);



	WARN_ON_ONCE(q->nr_blkgs[plid] <= 0);

	q->nr_blkgs[plid]--;



	/*

	 * Put the reference taken at the time of creation so that when all

	 * queues are gone, group can be destroyed.

	 */

	blkg_put(blkg);

}



void blkg_destroy_all(struct request_queue *q, enum blkio_policy_id plid,

		      bool destroy_root)

{

	struct blkio_group *blkg, *n;



	while (true) {

		bool done = true;



		spin_lock(&blkio_list_lock);

		spin_lock_irq(q->queue_lock);



		list_for_each_entry_safe(blkg, n, &q->blkg_list[plid],

					 q_node[plid]) {

			/* skip root? */

			if (!destroy_root && blkg->blkcg == &blkio_root_cgroup)

				continue;



			/*

		 * clear_queue_fn() might return with non-empty group list

		 * if it raced cgroup removal and lost.  cgroup removal is

		 * guaranteed to make forward progress and retrying after a

		 * while is enough.  This ugliness is scheduled to be

		 * removed after locking update.

			 * If cgroup removal path got to blk_group first

			 * and removed it from cgroup list, then it will

			 * take care of destroying cfqg also.

			 */

		list_for_each_entry(pol, &blkio_list, list)

			if (!pol->ops.blkio_clear_queue_fn(q))

			if (!blkiocg_del_blkio_group(blkg))

				blkg_destroy(blkg, plid);

			else

				done = false;

		}



		spin_unlock_irq(q->queue_lock);

		spin_unlock(&blkio_list_lock);



		/*

		 * Group list may not be empty if we raced cgroup removal

		 * and lost.  cgroup removal is guaranteed to make forward

		 * progress and retrying after a while is enough.  This

		 * ugliness is scheduled to be removed after locking

		 * update.

		 */

		if (done)

			break;



		msleep(10);	/* just some random duration I like */

	}

}

EXPORT_SYMBOL_GPL(blkg_destroy_all);



static void blkg_rcu_free(struct rcu_head *rcu_head)

{
@@ -1549,11 +1585,13 @@ static int blkiocg_pre_destroy(struct cgroup_subsys *subsys, 
		 * this event.

		 */

		spin_lock(&blkio_list_lock);

		spin_lock_irqsave(q->queue_lock, flags);

		list_for_each_entry(blkiop, &blkio_list, list) {

			if (blkiop->plid != blkg->plid)

				continue;

			blkiop->ops.blkio_unlink_group_fn(q, blkg);

			blkg_destroy(blkg, blkiop->plid);

		}

		spin_unlock_irqrestore(q->queue_lock, flags);

		spin_unlock(&blkio_list_lock);

	} while (1);
@@ -1695,12 +1733,14 @@ static void blkcg_bypass_start(void) 
	__acquires(&all_q_mutex)

{

	struct request_queue *q;

	int i;



	mutex_lock(&all_q_mutex);



	list_for_each_entry(q, &all_q_list, all_q_node) {

		blk_queue_bypass_start(q);

		blkg_destroy_all(q);

		for (i = 0; i < BLKIO_NR_POLICIES; i++)

			blkg_destroy_all(q, i, false);

	}

}

block/blk-cgroup.h

+5 −10
Original line number Diff line number Diff line
@@ -196,11 +196,6 @@ struct blkio_group { 
};



typedef void (blkio_init_group_fn)(struct blkio_group *blkg);

typedef void (blkio_link_group_fn)(struct request_queue *q,

			struct blkio_group *blkg);

typedef void (blkio_unlink_group_fn)(struct request_queue *q,

			struct blkio_group *blkg);

typedef bool (blkio_clear_queue_fn)(struct request_queue *q);

typedef void (blkio_update_group_weight_fn)(struct request_queue *q,

			struct blkio_group *blkg, unsigned int weight);

typedef void (blkio_update_group_read_bps_fn)(struct request_queue *q,
@@ -214,9 +209,6 @@ typedef void (blkio_update_group_write_iops_fn)(struct request_queue *q, 


struct blkio_policy_ops {

	blkio_init_group_fn *blkio_init_group_fn;

	blkio_link_group_fn *blkio_link_group_fn;

	blkio_unlink_group_fn *blkio_unlink_group_fn;

	blkio_clear_queue_fn *blkio_clear_queue_fn;

	blkio_update_group_weight_fn *blkio_update_group_weight_fn;

	blkio_update_group_read_bps_fn *blkio_update_group_read_bps_fn;

	blkio_update_group_write_bps_fn *blkio_update_group_write_bps_fn;
@@ -238,7 +230,8 @@ extern void blkcg_exit_queue(struct request_queue *q); 
/* Blkio controller policy registration */

extern void blkio_policy_register(struct blkio_policy_type *);

extern void blkio_policy_unregister(struct blkio_policy_type *);

extern void blkg_destroy_all(struct request_queue *q);

extern void blkg_destroy_all(struct request_queue *q,

			     enum blkio_policy_id plid, bool destroy_root);



/**

 * blkg_to_pdata - get policy private data
@@ -319,7 +312,9 @@ static inline void blkcg_drain_queue(struct request_queue *q) { } 
static inline void blkcg_exit_queue(struct request_queue *q) { }

static inline void blkio_policy_register(struct blkio_policy_type *blkiop) { }

static inline void blkio_policy_unregister(struct blkio_policy_type *blkiop) { }

static inline void blkg_destroy_all(struct request_queue *q) { }

static inline void blkg_destroy_all(struct request_queue *q,

				    enum blkio_policy_id plid,

				    bool destory_root) { }



static inline void *blkg_to_pdata(struct blkio_group *blkg,

				struct blkio_policy_type *pol) { return NULL; }

block/blk-throttle.c

+2 −97
Original line number Diff line number Diff line
@@ -157,14 +157,6 @@ static void throtl_init_blkio_group(struct blkio_group *blkg) 
	tg->iops[WRITE] = -1;

}



static void throtl_link_blkio_group(struct request_queue *q,

				    struct blkio_group *blkg)

{

	list_add(&blkg->q_node[BLKIO_POLICY_THROTL],

		 &q->blkg_list[BLKIO_POLICY_THROTL]);

	q->nr_blkgs[BLKIO_POLICY_THROTL]++;

}



static struct

throtl_grp *throtl_lookup_tg(struct throtl_data *td, struct blkio_cgroup *blkcg)

{
@@ -813,89 +805,6 @@ throtl_schedule_delayed_work(struct throtl_data *td, unsigned long delay) 
	}

}



static void

throtl_destroy_tg(struct throtl_data *td, struct throtl_grp *tg)

{

	struct blkio_group *blkg = tg_to_blkg(tg);



	/* Something wrong if we are trying to remove same group twice */

	WARN_ON_ONCE(list_empty(&blkg->q_node[BLKIO_POLICY_THROTL]));



	list_del_init(&blkg->q_node[BLKIO_POLICY_THROTL]);



	/*

	 * Put the reference taken at the time of creation so that when all

	 * queues are gone, group can be destroyed.

	 */

	blkg_put(tg_to_blkg(tg));

	td->queue->nr_blkgs[BLKIO_POLICY_THROTL]--;

}



static bool throtl_release_tgs(struct throtl_data *td, bool release_root)

{

	struct request_queue *q = td->queue;

	struct blkio_group *blkg, *n;

	bool empty = true;



	list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_THROTL],

				 q_node[BLKIO_POLICY_THROTL]) {

		struct throtl_grp *tg = blkg_to_tg(blkg);



		/* skip root? */

		if (!release_root && tg == td->root_tg)

			continue;



		/*

		 * If cgroup removal path got to blk_group first and removed

		 * it from cgroup list, then it will take care of destroying

		 * cfqg also.

		 */

		if (!blkiocg_del_blkio_group(blkg))

			throtl_destroy_tg(td, tg);

		else

			empty = false;

	}

	return empty;

}



/*

 * Blk cgroup controller notification saying that blkio_group object is being

 * delinked as associated cgroup object is going away. That also means that

 * no new IO will come in this group. So get rid of this group as soon as

 * any pending IO in the group is finished.

 *

 * This function is called under rcu_read_lock(). @q is the rcu protected

 * pointer. That means @q is a valid request_queue pointer as long as we

 * are rcu read lock.

 *

 * @q was fetched from blkio_group under blkio_cgroup->lock. That means

 * it should not be NULL as even if queue was going away, cgroup deltion

 * path got to it first.

 */

void throtl_unlink_blkio_group(struct request_queue *q,

			       struct blkio_group *blkg)

{

	unsigned long flags;



	spin_lock_irqsave(q->queue_lock, flags);

	throtl_destroy_tg(q->td, blkg_to_tg(blkg));

	spin_unlock_irqrestore(q->queue_lock, flags);

}



static bool throtl_clear_queue(struct request_queue *q)

{

	lockdep_assert_held(q->queue_lock);



	/*

	 * Clear tgs but leave the root one alone.  This is necessary

	 * because root_tg is expected to be persistent and safe because

	 * blk-throtl can never be disabled while @q is alive.  This is a

	 * kludge to prepare for unified blkg.  This whole function will be

	 * removed soon.

	 */

	return throtl_release_tgs(q->td, false);

}



static void throtl_update_blkio_group_common(struct throtl_data *td,

				struct throtl_grp *tg)

{
@@ -960,9 +869,6 @@ static void throtl_shutdown_wq(struct request_queue *q) 
static struct blkio_policy_type blkio_policy_throtl = {

	.ops = {

		.blkio_init_group_fn = throtl_init_blkio_group,

		.blkio_link_group_fn = throtl_link_blkio_group,

		.blkio_unlink_group_fn = throtl_unlink_blkio_group,

		.blkio_clear_queue_fn = throtl_clear_queue,

		.blkio_update_group_read_bps_fn =

					throtl_update_blkio_group_read_bps,

		.blkio_update_group_write_bps_fn =
@@ -1148,12 +1054,11 @@ void blk_throtl_exit(struct request_queue *q) 


	throtl_shutdown_wq(q);



	spin_lock_irq(q->queue_lock);

	throtl_release_tgs(td, true);

	blkg_destroy_all(q, BLKIO_POLICY_THROTL, true);



	/* If there are other groups */

	spin_lock_irq(q->queue_lock);

	wait = q->nr_blkgs[BLKIO_POLICY_THROTL];



	spin_unlock_irq(q->queue_lock);



	/*

block/cfq-iosched.c

+6 −94
Original line number Diff line number Diff line
@@ -1045,14 +1045,6 @@ static void cfq_update_blkio_group_weight(struct request_queue *q, 
	cfqg->needs_update = true;

}



static void cfq_link_blkio_group(struct request_queue *q,

				 struct blkio_group *blkg)

{

	list_add(&blkg->q_node[BLKIO_POLICY_PROP],

		 &q->blkg_list[BLKIO_POLICY_PROP]);

	q->nr_blkgs[BLKIO_POLICY_PROP]++;

}



static void cfq_init_blkio_group(struct blkio_group *blkg)

{

	struct cfq_group *cfqg = blkg_to_cfqg(blkg);
@@ -1096,84 +1088,6 @@ static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) 
	blkg_get(cfqg_to_blkg(cfqg));

}



static void cfq_destroy_cfqg(struct cfq_data *cfqd, struct cfq_group *cfqg)

{

	struct blkio_group *blkg = cfqg_to_blkg(cfqg);



	/* Something wrong if we are trying to remove same group twice */

	BUG_ON(list_empty(&blkg->q_node[BLKIO_POLICY_PROP]));



	list_del_init(&blkg->q_node[BLKIO_POLICY_PROP]);



	BUG_ON(cfqd->queue->nr_blkgs[BLKIO_POLICY_PROP] <= 0);

	cfqd->queue->nr_blkgs[BLKIO_POLICY_PROP]--;



	/*

	 * Put the reference taken at the time of creation so that when all

	 * queues are gone, group can be destroyed.

	 */

	blkg_put(cfqg_to_blkg(cfqg));

}



static bool cfq_release_cfq_groups(struct cfq_data *cfqd)

{

	struct request_queue *q = cfqd->queue;

	struct blkio_group *blkg, *n;

	bool empty = true;



	list_for_each_entry_safe(blkg, n, &q->blkg_list[BLKIO_POLICY_PROP],

				 q_node[BLKIO_POLICY_PROP]) {

		/*

		 * If cgroup removal path got to blk_group first and removed

		 * it from cgroup list, then it will take care of destroying

		 * cfqg also.

		 */

		if (!cfq_blkiocg_del_blkio_group(blkg))

			cfq_destroy_cfqg(cfqd, blkg_to_cfqg(blkg));

		else

			empty = false;

	}

	return empty;

}



/*

 * Blk cgroup controller notification saying that blkio_group object is being

 * delinked as associated cgroup object is going away. That also means that

 * no new IO will come in this group. So get rid of this group as soon as

 * any pending IO in the group is finished.

 *

 * This function is called under rcu_read_lock(). key is the rcu protected

 * pointer. That means @q is a valid request_queue pointer as long as we

 * are rcu read lock.

 *

 * @q was fetched from blkio_group under blkio_cgroup->lock. That means

 * it should not be NULL as even if elevator was exiting, cgroup deltion

 * path got to it first.

 */

static void cfq_unlink_blkio_group(struct request_queue *q,

				   struct blkio_group *blkg)

{

	struct cfq_data *cfqd = q->elevator->elevator_data;

	unsigned long flags;



	spin_lock_irqsave(q->queue_lock, flags);

	cfq_destroy_cfqg(cfqd, blkg_to_cfqg(blkg));

	spin_unlock_irqrestore(q->queue_lock, flags);

}



static struct elevator_type iosched_cfq;



static bool cfq_clear_queue(struct request_queue *q)

{

	lockdep_assert_held(q->queue_lock);



	/* shoot down blkgs iff the current elevator is cfq */

	if (!q->elevator || q->elevator->type != &iosched_cfq)

		return true;



	return cfq_release_cfq_groups(q->elevator->elevator_data);

}



#else /* GROUP_IOSCHED */

static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,

						struct blkio_cgroup *blkcg)
@@ -1186,8 +1100,6 @@ cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) { 
	cfqq->cfqg = cfqg;

}



static void cfq_release_cfq_groups(struct cfq_data *cfqd) {}



#endif /* GROUP_IOSCHED */



/*
@@ -3547,17 +3459,20 @@ static void cfq_exit_queue(struct elevator_queue *e) 
		__cfq_slice_expired(cfqd, cfqd->active_queue, 0);



	cfq_put_async_queues(cfqd);

	cfq_release_cfq_groups(cfqd);



	spin_unlock_irq(q->queue_lock);



	blkg_destroy_all(q, BLKIO_POLICY_PROP, true);



#ifdef CONFIG_BLK_CGROUP

	/*

	 * If there are groups which we could not unlink from blkcg list,

	 * wait for a rcu period for them to be freed.

	 */

	spin_lock_irq(q->queue_lock);

	wait = q->nr_blkgs[BLKIO_POLICY_PROP];

#endif

	spin_unlock_irq(q->queue_lock);



#endif

	cfq_shutdown_timer_wq(cfqd);



	/*
@@ -3794,9 +3709,6 @@ static struct elevator_type iosched_cfq = { 
static struct blkio_policy_type blkio_policy_cfq = {

	.ops = {

		.blkio_init_group_fn =		cfq_init_blkio_group,

		.blkio_link_group_fn =		cfq_link_blkio_group,

		.blkio_unlink_group_fn =	cfq_unlink_blkio_group,

		.blkio_clear_queue_fn = cfq_clear_queue,

		.blkio_update_group_weight_fn =	cfq_update_blkio_group_weight,

	},

	.plid = BLKIO_POLICY_PROP,

block/elevator.c

+3 −2
Original line number Diff line number Diff line
@@ -876,7 +876,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 
{

	struct elevator_queue *old = q->elevator;

	bool registered = old->registered;

	int err;

	int i, err;



	/*

	 * Turn on BYPASS and drain all requests w/ elevator private data.
@@ -895,7 +895,8 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e) 
	ioc_clear_queue(q);

	spin_unlock_irq(q->queue_lock);



	blkg_destroy_all(q);

	for (i = 0; i < BLKIO_NR_POLICIES; i++)

		blkg_destroy_all(q, i, false);



	/* allocate, init and register new elevator */

	err = -ENOMEM;